Stage IA invasive lobular breast cancer with ipsilateral marginal zone lymphoma: no recurrence after surgery and radiation

What happened, in summary

This 78-year-old woman had no family history of breast cancer and did not feel a breast lump herself. Her cancers were found after an abnormal screening mammogram. Diagnostic mammogram and ultrasound showed several right breast findings, including a small lesion at 1 o'clock and another suspicious mass at 10 o'clock. Biopsy of the 1 o'clock lesion showed a low-grade B-cell lymphoproliferative disorder favoring marginal zone lymphoma. The lymphoma markers included CD20 and Bcl-2 positivity, partial CD43 positivity, low Ki-67 under 10%, clonal IGH rearrangement, and no MALT1 rearrangement. Re-biopsy of the 10 o'clock lesion showed invasive lobular carcinoma, Nottingham grade 1, ER 95% positive, PR-negative, and HER2/neu negative. Breast MRI measured the invasive lobular carcinoma at 2.3 cm and the lymphoma at 1.0 cm. PET-CT did not show FDG-avid locoregional or distant disease. The marginal zone lymphoma was staged IAE, and surgery later showed the breast cancer was Stage IA, pT1bN0(sn)cM0. She chose breast-conserving surgery with segmental mastectomy and sentinel lymph node biopsy for the invasive lobular carcinoma. Final pathology showed a 6 mm tumor, clear margins, no lymphovascular invasion, and 2 negative sentinel nodes. She then received right whole-breast radiation therapy, 40.05 Gy in 15 fractions, a dose chosen to treat both the breast cancer and the lymphoma in the same breast. She developed grade 1 dermatitis that improved with topical mometasone. A later cough prompted evaluation, but imaging did not show pneumonia, radiation pneumonitis, or pulmonary embolism. As of May 2025, five-month follow-up mammogram and clinical assessment showed no recurrence.